title: Improved light harvesting and improved efficiency by insertion of an optical spacer (ZnO) in solution-processed small-molecule solar cells.
abstract: We demonstrate that the power conversion efficiency can be significantly improved in solution-processed small-molecule solar cells by tuning the thickness of the active layer and inserting an optical spacer (ZnO) between the active layer and the Al electrode. The enhancement in light absorption in the cell was measured with UV-vis absorption spectroscopy and by measurements of the photoinduced carriers generation rate. The ZnO layer used to improve the light-harvesting increases the charge collection efficiency, serves as a blocking layer for holes, and reduces the recombination rate. The combined optical and electrical improvements raise the power conversion efficiency of solution-processed small-molecule solar cells to 8.9%, that is, comparable to that of polymer counterparts.
authors.affiliation: Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106-5090, United States.
authors.forename: Aung Ko Ko
authors.initials: AK
authors.lastname: Kyaw
authors.forename: Dong Hwan
authors.initials: DH
authors.lastname: Wang
authors.forename: David
authors.initials: D
authors.lastname: Wynands
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Thuc-Quyen
authors.initials: TQ
authors.lastname: Nguyen
authors.forename: Guillermo C
authors.initials: GC
authors.lastname: Bazan
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Heeger